Respiratory muscle weakness in facioscapulohumeral muscular dystrophy

Abstract

Introduction: The purpose of this study was to comprehensively evaluate respiratory muscle function in adults with facioscapulohumeral muscular dystrophy (FSHD). Methods: Fourteen patients with FSHD (9 men, 53 ± 16 years of age) and 14 matched controls underwent spirometry, diaphragm ultrasound, and measurement of twitch gastric and transdiaphragmatic pressures (twPgas and twPdi; n = 10) after magnetic stimulation of the lower thoracic nerve roots and the phrenic nerves. The latter was combined with recording of diaphragm compound muscle action potentials (CMAPs; n = 14). Results: The following parameters were significantly lower in patients vs controls: forced vital capacity (FVC); maximum inspiratory and expiratory pressure; peak cough flow; diaphragm excursion amplitude; and thickening ratio on ultrasound, twPdi (11 ± 5 vs 20 ± 6 cmH2O) and twPgas (7 ± 3 vs 25 ± 20 cmH2O). Diaphragm CMAP showed no group differences. FVC correlated inversely with the clinical severity scale score (r = −0.63, P =.02). Discussion: In FSHD, respiratory muscle weakness involves both the diaphragm and the expiratory abdominal muscles.